A conventional string-set of series connected decorative lamps is composed of a 120 V AC power plug and multiple small sockets able to accept bulbs. As previously stated, the typical string of X'mas tree light is usually found to be 35 or 50 lights per string. All of the light bulbs are connected in series to a 120 V AC supply. Although a conventional string-set can also serve as an decorative item, its monotonous variation in lighting seems not attractive enough.
Referring to U.S. Pat. No. 4,682,079 granted to Sanders et al, in which the new design of string-set provides a renovated circuit which can transfer AC power source to DC source for a DC motor to drive some small-size acting decorative means. The major defect of this patent is to use too many electronic elements which raise production cost and thereby production defect. Apart from this, an operating DC motor is very noisy and has higher percentage of defectives than those for an AC motor.
As for another example, U.S. Pat. No. 4,980,608 granted to Morrison, which involves a small AC motor connected with strings in series so as to rotate a small suspending ornament. In this patent, the major method applied is to design an AC motor which impedance could be the same as the light bulb and therefore interchangeable in the light string. The major defect of this patent is that the torque of the motor is excessively small (about 0.070 kgw/cm). The output torque of the motor is limited and only small suspending ornament can be rotated, because the current through the bulbs is in the range of 0.120 to 0.210 amperes and the impedance of the AC motor is equivalent to the light bulb. If it is desired a larger transmission means of a doll to be driven, this motor will fail.